The present invention relates to an adjusting device for magnetic heads in a magnetic recording/reproducing apparatus and, more particularly, to an adjusting device for magnetic heads which require an adjustment of position in the direction of running of the magnetic recording medium.
Generally, in a magnetic recording/reproducing apparatus for video signals, a magnetic tape runs from a reel to a rotary head cylinder having a rotary video head via a tape guide pin, eraser head and so forth and, after having been wound around the rotary head cylinder, runs past an audio control head, tape guide pin, capstan and so forth to another reel. For reproducing video or audio signals from a magnetic tape with this tape running system, it is often required to adjust the position of the magnetic head in order that the control head correctly traces the control pulses recorded on the control track on the magnetic tape.
In, for example, Japanese Utility model Laid-Open Publication No. 39523/80 (Application No. 120563/78, filed on Sept. 4, 1978), a device for adjusting the position of the magnetic head is proposed wherein a support and position adjustment for a magnetic head block, usually referred to as "ACE head" in which a magnetic heads for audio signal and control signal and a magnetic head for erasing audio track are constructed as a single unit. In this proposed construction, independent adjustments of not only the position of the magnetic head in the direction of running of the tape but also other adjustment items such as the azimuth angle of the head gap, height of the head, the tilt (inclination) of the head in the back and forth direction and so forth.
While adjustment of an azimuth angle and the adjustment of the position of the head in the tape running direction can be made independently of other items of adjustment. The adjustment of the tilt of the head and the adjustment of the head height, however, affect the azimuth angle and the head position in the tape running position, respectively.
No problem will be caused if predetermined sequences of adjustments are followed, namely, adjustment of the azimuth angle after adjustment of the tilt of the head and adjustment of magnetic head in the tape running direction after the adjustment of magnetic head height. However, with readjustment of a height of the head or readjustment of the tilt of the head, it is necessary to make troublesome readjustment of the head position in the tape running direction or of the azimuth angle even if the head position or the tilt of the head has been correctly adjusted. Without the subsequent readjustment of the head position in the tape running direction or the azimuth angle, problems arise due to incorrect adjustment.
In recent years, there has been a remarkable improvement in the performance which, in turn, affords a higher density in recording on a magnetic tape. Consequently, the tape running speed suitable for the recording or reproduction has been decreased to 1/2 and then to 1/3 of that required before. The decrease in the tape running speed has imposed a new problem namely, the azimuth angle is now seriously affected by a slight play in the fit between the support shaft and the associated sleeve. For instance, assuming that the track width is 1 mm and the recording frequency is 4 KHz, the level of azimuth loss due to 5' (minutes) deviation of azimuth angle was as small as about -0.4dB when the tape running speed was 33.35 mm. However, when the tape running speed is reduced to 11.12 mm which is about 1/3 (one third), a large azimuth loss of about -4.3dB is caused by the same deviation of the azimuth angle. For instance, the deviation of 5' is caused even by a small inclination of the support shaft caused by a minute clearance of 36 .mu.m between the support shaft and the shaft hole when the axial length of fit between the sleeve and the support shaft is 25 mm. In order to reduce the azimuth loss down to the level of -0.4dB at the low tape speed of 11.12 mm, it is necessary to reduce the clearance between the support shaft and the shaft hole to a level of 12 .mu.m which can hardly be attained by ordinary machining. Clearly, it is quite costly to realize a fit which has small clearance between two members but still ensuring smooth relative sliding motion therebetween.